This invention relates in general to drive train systems for transferring rotational power from a source to a driven mechanism, such as from a vehicular engine/transmission assembly to an axle assembly. In particular, this invention relates to an improved structure for a driveshaft assembly for use in such a drive train system that is balanced for rotation during use, and to a method of manufacturing same.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a typical driveshaft assembly includes a hollow cylindrical driveshaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends thereof. The front end fitting forms a portion of a front universal joint that connects the output shaft of the engine/transmission assembly to the front end of the driveshaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint that connects the rear end of the driveshaft tube to the input shaft of the axle assembly. The front and rear universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.
Ideally, the driveshaft tube would be formed in the shape of a cylinder that is absolutely round, absolutely straight, and has an absolutely uniform wall thickness. Such a perfectly shaped driveshaft tube would be precisely balanced for rotation and, therefore, would not generate any undesirable noise or vibration during use. In actual practice, however, the driveshaft tube and other components of the driveshaft assembly usually contain variations in roundness, straightness, and wall thickness that result in minor imbalances when rotated at high speeds. To prevent such imbalances from generating undesirable noise or vibration when rotated during use, it is commonplace to counteract such imbalances by securing balance weights to selected portions of the driveshaft tube or other components of the driveshaft assembly. The balance weights are sized and positioned to counterbalance the imbalances of the driveshaft assembly such that it is balanced for rotation during use.
Traditionally, the balancing process has been performed with the use of a conventional balancing machine. A typical balancing machine includes a pair of fittings that are adapted to support the ends of the driveshaft assembly thereon. The balancing machine further includes a motor for rotating the driveshaft assembly at a predetermined speed. As the driveshaft assembly is rotated, the balancing machine senses vibrations that are caused by imbalances in the structure of the driveshaft assembly. The balancing machine is responsive to such vibrations for determining the size and location of one or more balance weights that, if secured to the driveshaft assembly, will minimize these imbalances. The rotation of the driveshaft assembly is then stopped to allow such balance weights to be secured to the outer surface of the driveshaft tube or other components of the driveshaft assembly in a conventional manner, such as by welding, adhesives, and the like. The driveshaft assembly is again rotated to confirm whether proper balance has been achieved or to determine if additional balance weights are required. A number of such balancing machines of this general structure and method of operation are known in the art.
In the past, vehicular driveshaft tubes have been formed from steel alloys or other metallic materials having relatively large wall thicknesses and having relatively high melting temperatures. In such driveshaft tubes, conventional welding processes have been commonly used to secure the balance weights directly thereto. Because of the relatively large wall thicknesses and relatively high melting temperatures of such driveshaft tubes, the heat generated during the welding process does not adversely distort the shape or affect the torque-transmitting capacity thereof in a significant manner. However, in some instances, it is desirable to form the driveshaft tubes having relatively small wall thicknesses or from materials having relatively low melting temperatures. For example, in racing vehicles, it may be desirable to minimize the wall thickness of the driveshaft tube to reduce weight. Also, it may be desirable to form the driveshaft tubes from aluminum alloys and other relatively lightweight metallic materials that have relatively low melting temperatures. The use of conventional welding processes to secure the balance weights directly to the driveshaft tubes in either of these instances is somewhat more difficult because the heat generated during the welding process may undesirably distort the shape or affect the torque-transmitting capacity thereof in a significant manner. Thus, it would be desirable to provide an improved structure for a driveshaft assembly for use in a drive train system that is balanced for rotation during use, and an improved method of manufacturing same, that avoids these problems.